No the folks in Placencia did something very well studied and ecological - I think they used logs actually. It was a really cool thing. I guess my point is that the groins tend to work, but you might need a permit to keep one. I've seen some subtle ones in play along the shore here - boulders under piers ....... they attract fish, hold sand, and are not "construction" in a way that excites people into court.
Indeed the beach on either side of the groyne grew - one more significantly than the other, but both benefitted.
I just realized I didn't completely explain the system yesterday. The sacks of cement/sand set up and get hard but because they are less than a foot above the water level when they are set in place when the rough seas go over the wall with the suspended sand it settles down because of the wall and the sand is deposited. BUT the most interesting thing is that it also covers the wall completely so it is not visible. It even raises the level of the sand 10 feet or so on the sea side so it is a gradual slope. And It stays that way even in future rough seas. Of course as I explained you can then add more height to the wall up to a point and keep going higher. It will only go so high depending on the physical situation of the location.
I found a few great photos that will show without a doubt this works but I don't know how to put them on the form. Tell me how to put them on or give me your email and I'll send them to you.